1. Field of the Invention
The present invention relates to a roadside narrowband wireless communication apparatus to be used for a road-to-vehicle narrowband wireless communication system.
2. Description of the Related Art
A road-to-vehicle narrowband wireless communication system for communicating various information between a narrowband wireless communication apparatus mounted on a vehicle traveling on a road and a roadside antenna apparatus installed on the road has been known. The road-to-vehicle narrowband wireless communication system is becoming capable of handling plural service systems in addition to communication relating to receipt of tolls by ETC, such as so-called VICS for offering traffic information, the Internet, and communication for various services in parking areas are handled.
Since the service systems are originally independently constructed systems, they are different in radio frequency, and it is difficult to make an on-board unit to be compatible with all the services by the use of one wireless antenna. However, it is difficult to provide plural antennas on a vehicle from the view points of limited space area, cost, and appearance Also, it is undesirable from the cost point of view to install the roadside narrowband wireless communication system for each of the services.
In FIG. 2 of JP-A-2001-103016, there is disclosed a system wherein an integrated base station 200 (called also as roadside apparatus) provided with a synthesis division unit 203 for multiplexing different wireless communication frequencies of services to form a common frequency to be transmitted as one frequency and dividing signals for the services after the transmission is installed as a superordinate station to a roadside antenna apparatus (referred to as a local base station 400 in JP-A-2001-103016). The system is capable of communicating to and from the roadside antenna apparatus the radio signals at the common frequency corresponding to the plural services through an optical fiber. In this case, a narrowband wireless communication apparatus mounted on a vehicle is provided with an antenna for the common frequency, a synthesis division unit for separating the signal into plural wireless frequencies corresponding to the original plural services, and plural wireless applications for the separated plural frequencies.
Since such communication service is subject to service type change, service type increase, or increase in number of vehicles allowed to use the service simultaneously, the roadside narrowband wireless communication system has to undergo alteration (hereinafter referred to as maintenance) of system so as to be in conformity with the change and increases from time to time. The system disclosed in JP-A-2001-103016 also requires such maintenance, and, in the case of maintenance, a worker must go to each of the roadside antenna apparatus installed roadside to perform tasks of setting changes and the like. Such maintenance has a cost problem due to the large number of roadside antenna apparatuses installed at an interval of several kilometers along a road and the distance between the adjacent apparatuses, i.e., since the maintenance requires a large number of workers and long time, that is, increased cost.
Also, since the system disclosed in JP-A-2001-103016 communicates signals of a carrier frequency (very high frequency) of a wireless communication between the system and a vehicle from the integrated base station 200 to each of local base stations 400 via the optical fiber, the system has a drawback that the transmission device is remarkably expensive.